Well for sure, the owner would have to agree to having the security instrument placed on the property. You can't place a mortgage on someone else's property. For practical matters, banks will NOT consider mortgages typically unless all the owners are part of the application, though they may consider others who are not owners as well. Still you will often not get favorable terms if all the applicants do not intend to owner-occupy the property. If you deed the property to the relative (in full or in part) to scam the bank, you can trigger a due-on-sale clause if you attempt to deed ownership away from those on the loan.